Durable, anticorrosive and attractive surface coatings with electrical contact application

ABSTRACT

Electrically functional and decorative surface coatings- which are durable, attractive in appearance and resistant to corrosion and most importantly have long-lasting retention of foregoing properties under service conditions- are produced by reactive absorption of unsaturated oils into oxides of certain metals and metal alloys. The oil-treated oxide surfaces- especially after periods of in-service use- have lower contact impedance, higher conductivity, better retention of appearance and greater resistance to wear and corrosion than the untreated oxides. It appears that a highly stable interfacial compound is formed between the oil, the oxide coating and possibly the unoxidized basic metallic material, which differs considerably from the oxide in stability and general physical composition. Existence of this compound is evidenced by the heightened ability of the treated finish to withstand corrosion and scratching, and the tendency of the finish to actually harden and acquire greater wear resistance and permanence of appearance with age.

waited States Fatent Denim, 51:. et al.

[ 51 Feb. 29, 1972 DURABLE, ANTKCORROSHVE AND ATTRACTHVE SURFACECOATHNGS WlTH-ll ELECTRIQAL CONTACT APPLHCATHON inventors: Eugene P.Damm, Jn; Allen W. Grobin,

Jun, both of Poughkeepsie; Edwin H.'

lllerel, Fishkill; David A. Radovsky, Poughkeepsie, all of N.Y.

International Business Machines Corporation, Armonk, NY.

Filed: July l, 1970 Appl. No.: 51,701

Assignee:

References Cited UNITED STATES PATENTS 11/1951 Ringk et a1 ..204/35 NPrimary ExaminerJohn H. Mack Assistant ExaminerW. 1. SolomonAttorneyl-lanifin and Jancin and Robert Lieber [57] ABSTRACTElectrically functional and decorative surface coatingswhich aredurable, attractive in appearance and resistant to corrosion and mostimportantly have long-lasting retention of foregoing properties underservice conditions-are produced by reactive absorption of unsaturatedoils into oxides of certain metals and metal alloys. The oil-treatedoxide surfacesespecially after periods of in-service usehave lowercontact impedance, higher conductivity, better retention of appearanceand greater resistance to wear and corrosion than the untreated oxides.It appears that a highly stable interfacial compound is formed betweenthe oil, the oxide coating and possibly the unoxidized basic metallicmaterial, which differs considerably from the oxide in stability andgeneral physical composition. Existence of this compound is evidenced bythe heightened ability of the treated finish to withstand corrosion andscratching, and the tendency of the finish to actually harden andacquire greater wear resistance and permanence of appearance with age.

7 Claims, No Drawings DURABLE, ANTICORROSIVE AND ATTRACTIVE SURFACECOATINGS WITH ELECTRICAL CONTACT APPLICATION BACKGROUND OF THE INVENTION1 Field of the Invention The invention pertains the production andutilization in electrical equipment of metal finishes which possesslong-life properties of: electrical functionality, decorativeness anduniformity of appearance, durability and anticorrosiveness. The processcomprises formation of an oxide film upon' the surface of a PO970-007selected metal or metal alloy, and the absorption into said oxide filmof an oil which reacts in an unexplained manner with the oxide to form along-lived compound having electrical functionality, for electricalcontact and conduction applications, and physical and decorationalproperties desirable for exterior equipment coatings. Materials sotreated are utilized for example as finish coatings upon steelelectronic equipment housings in order to provide attractive externalfinishes having electrical continuity for electromagnetic shielding ofthe internal electronics.

2. Description of the Prior Art The decorational, anticorrosive andprotective properties of certain oiled or lacquered metallic oxidefinishes are well known and have been extensively investigated byworkers in the metal finishing arts. Kerr and MacNaughton (TechnicalPublications of the International Tin Research and Development Counsel,Series A, No. 48, 1937, particularly pages 1-7), Fishlock (MetalColoring," Robert Draper LTD, 1962 especially pages 188-191 and 282283)and others have disclosed the coloring and covering properties of anodicoxides of such metals as tin and aluminum, and the additional protectionafiorded by lacquering or oiling. However such finishes have not beenconsidered for electrical contact and/or conduction applications; quitepossibly because the untreated oxides are known to be unstable and thefinishing oils and lacquers are known to be insulators.

Accordingly our invention resides in the discovery and application ofthe long-life electrical conduction and decorational appearanceproperties of certain oil treated metallic oxide surface coatings.

SUMMARY The invention concerns recognition that reaction of certainmetallic oxides with oils having specific unsaturated constituentsproduces distinctive long-lived compounds especially useful asdecorative conductors of electricity which are exposed to view inelectrical equipment. The low-contact impedance and other electrical andphysical properties of these compounds are used to particular advantagein producing ground shield coatings upon frames and panels of electronicequipment. Other properties of these compounds are highconductivity,durability, anticorrosiveness, resistance to scratching and attractivecolored matte appearance.

A noteworthy aspect of the durability feature is that it improves withinitial aging of the oil treated finish.

Treated metals which exhibit the foregoing properties after oxidationand oil treatment include tin, lead, indium, and alloys containing atleast one of these.

Oils compounded with the foregoing metals in the finishing treatmentinclude the linseed oils (raw, blown, boiled, heat bodied), tung oil,soybean oil, rapeseed oil, dehydrated castor oil, corn oil, peanut oil,lard oil, cottonseed oil, orticica oil, and sunflower seed oil. Theseare believed to be only representative of a larger class of vegetable,animal and other oils containing as common constituent an acid in theduodecanoic, octadecanoic, octadecadienoic, octadecatrienoic,eleostearic, licanic or docosoenic classes. Properties of the compoundare treated in the following description of specific examples.

DETAILED DESCRIPTION Material requirements in the electrical industryare becoming increasingly sophisticated and complex. For example thephysically connected frames and covers of modular sections of dataprocessing systems are required to serve both as protective housingswith attractive external appearance and as electrically continuouselectromagnetic shields. A requirement that touching sections presentcontact impedances les than one ohm to electrical signals in a frequencyrange from DC to above 30 MHz is not considered uncommon.

We have found that surface compounds formed in the manner describedherein are capable of satisfying all of the foregoing electrical,protective and decorative requirements.

We have discovered that when tin, lead, indium and alloys containing atleast one of these metals are anodized as taught by Kerr and MacNaughtonabove, to form a dark colored finish having decorative appearance, andthen treated with an absorbed layer of oil, not only is the dried finishnot oily to the touch but it possesses a number of interestingelectrical, physical and decorational properties not coincidentallypossessed by the untreated oxide or by any other materials known to us.We have noted especially that when unsaturated oils, that is oils havingcomponents with double or triple bonds, are utilized in such treatmentthe dried finish acquires and retains a pleasing finish and highlyuseful electrical contact impedance and conduction properties. Moreimportantly the finish and electrical quality are highly stable eventhough the untreated material may be basically unstable with respect tothese properties. Thus the oil-treated finishes have numerous potentialapplications not hitherto considered for the untreated material becauseof the known instability of the latter.

' The treated oxide surfaces have color uniformity of a surprisinglyhigh order and resistance to corrosion, scratching and other physicaldamage also of a surprisingly high order.

A possible explanation for the improved stability of the treated finishis that a chemical reaction occurs between the substrate, the anodicoxide layer and the unsaturated oil by which an electrically conductivenew compound is formed. This appears to be unusual because the oils usedand certain of the oxides are basically insulators. Thus we understandthat the oil is not merely a pore closing agent.

It is of course not the intent here to claim that the formation of acompound between a metallic oxide layer and another substance is per sean inventive discovery. It has long been recognized that oxidized metalscan be reacted with other substances to form compounds in structure fromthe untreated oxide. Representative of such recognition would be thedisclosure for example in US. Pat. No. 2,574,225 by Ringk et al.,concerning oxides of aluminum, magnesium, tin, zinc, and their alloys.When treated with 8-quinolinol or its salts these are said to form acompound having resistance to attack by bacteria fungus and the like,notwithstanding the absence of such property in the oxidized butuntreated metal.

On the contrary our invention resides primarily in the recognition thatthe compounds formed by the particular treatments enumerated herein havea combination of high stability electrical, decorational andprotectional coating properties, which is unique and especiallydesirable for exposed electrical conduction applications.

The following discussion of examples will help to illustrate thepractice of this invention and the advantages derived therefrom. Itshould be understood however that the purpose of the discussion is onlyillustrative and not limiting.

EXAMPLES l Tin plate (.0006 inches thick) on steel substrate isanodically oxidized to a surface depth of 0.0001 inch by the method ofKerr and MacNaughton supra. The oxide outer layers of several samplesare reacted with foregoing oils (the term reacted" is employed for wantof better terms to describe the desired effect which is the completeincorporation or absorption of the oil into the outer oxide layerleaving no excess of oil on the surface), excess oil being permitted todrain freely off the treated samples. Each oil is applied by immersionof the samples. The oil bath is at room temperature.

Electrical quality (contact impedance) and appearance are observedbefore and after exposure of the samples to standard acceleratedenvironmental aging processes (77 days of cyclically repeatedtemperature humidity cycles: 4 hours at 77 F./50% Rl-l, 4 hours at 150F./90% RH, 16 hours at 150 F./50% RH) which are supposed to approximateclosely in effect multiple years of field use under average in-serviceoperational and environmental conditions. Tables I and 11 below indicaterespectively sample properties before and after aging.

TABLE IV Unaged indium-lead oxide samples.

Contact ohms at Untreated Boiled Linseed Oil 1 MHz 0.501 0.026 MHz 0.9500.165 MHZ 0.950 0.390 Appearance Black Matte Black Matte Note superiorelectrical quality of treated sample.

TABLE I.PREAGED SAMPLES TIN OXIDE ON TIN ON STEEL Sample number Dehy-Saturated Boiled Refined Oitidratcd Rape lubricating linseed Tallsoybean cia Tung castor seed Treating 011 None 011 No. 2 oil oil oil oiloil oil 011 Contact impedance ohms lMllz 0.095 1.970 0.016 0.175 0.0160.004 0.069 0.023 0.023

IOMHZH... 0.178 5. 761 0.120 0.120 0.105 0.145 0.145 0.125 0.175

30 Mllz .7 0.470 0.836 0.330 0. 340 0. 300 0.360 0.360 0.350 0.500

Appearance, dryness Uniform black dull matte attractive finish, allsamples. Sample No. 2 oily to touch; others dry Denotes control sample.

TABLE II.SAME SAMPLES AS TABLE IAFTER ACCELERAIED AGING PROCESS Samplenumber 1,000 0. 247 0.025 0.150 0.046 0. 060 0.080 0.052 0.034 1, 000 0.234 0.180 0. 205 0.115 0.145 0.155 0.135 0.180 1,000 0. 389 0.480 0. 3800.310 0.360 0.370 0.360 0. 500 Appearance, dryness N0 changethcsesamples 1 Rusty, no black. 2 Colorless metallic tin; still oily.

Observe electrical and physical instability of Sample No. 1 EXAMPLES 5 fg g phgslcal j lfi gl fi f Indium oxide (0.0001 inch) anodized on indiumsheet i 0 amp 6 (Samp 6 tea 6 W1 lg y Sa (0.005 inch) per Examples 1.Preand postaging electrical rate qualities similar (less than 1 ohm) foruntreated and boiled lin- EXAMPLES 2 seed oil reacted samples. Howeverafter aging untreated sample appearance reverted from black matte tometallic silvery Lead OXlde Inches) on surface Oflead Sheet ((1005color, whereas treated sample retained uniform black matte inches)formed by anodizing process same as in Examples 1. fi i h TABLE II!EXAMPLES 6 Lead oxide unaged samplesExamples 2 Sample treated Observepoor electrical quality and appearance of control for electrical panelfinish applications.

EXAMPLES 3 Oxide surface layer (0.0001 inches) in 5% indium, 95% lead(.003 inches) plate on copper sheet formed by anodizing process same asExamples 1.

Black tin oxide (0.7 inches) on tin (0.7 inches) on steel. Results sameas for Examples 1.

EXAMPLES 7 Black oxides of 60-40 tin-lead alloy and 37 37 /z25 tinleadindium alloys, obtained by anodic treatment as in Examples l, were foundto possess similar electrical qualities (lowohms contact impedance l30MHz) with or without boiled linseed oil treatment, and before and afteraccelerated aging. However after aging, samples not treated with oilshowed tendency to lose color. Where oil treated samples retainedconsistent appearance. Also tin-lead alloy samples not treated with oilhad postaging contact impedance greater than 1 ohm but less than 10 ohmswhere all other samples gave corresponding impedance readings below 1ohm.

Some of foregoing tin and tin alloy examples had small traces ofimpurities such as bismuth, antimony, nickel, etc. Control experimentswith 99.99 percent pure tin oxide-tin indicated that such impurities donot affect conclusions to be drawn from oil treatment and aging processresults considered above.

Of particular interest is the fact that the oil treated oxides aboverequire and stably retain the above useful electrical properties anduniform matte appearance even in instances where the unoxidized materialis a poor conductor.

We have shown and described above the fundamental novel features of theinvention as applied to several preferred embodiments. It will beunderstood that various omissions, substitutions and changes in form anddetail of the invention as described herein may be made by those skilledin the art without departing from the true spirit and scope of theinvention. It is the intention therefore to be limited only by the scopeof the following claims.

What is claimed is:

1. An article having a surface possessing properties of lowelectricalcontact impedance, attractiveness, and corrosion resistance, allretained stably over extended periods of service usage, formed by thereaction product of an anodized surface layer of a metal selected fromthe class consisting of tin, lead, indium, and alloys containing atleast one of the foregoing metals, with an absorbed oil having anunsaturated constituent.

2. In electrical equipment an exterior panel and frame finish coatingcomprising a conductive compound formed by reaction of an anodized layerof a metal with an absorbed layer of a reactive oil wherein said metalis selected from the class consisting of tin, lead, indium and alloyscontaining at least one of these metals and wherein the said oil has anunsaturated constituent.

3. Coating of claim 2 wherein said anodized layer is formed by anodicoxidization of a thin surface layer of said metal or metal alloysupported upon a substrate o f anotlrgmetal.

4. A process for treating surfaces composed of tin, lead, indium, oralloys formed from combinations thereof, in order to establish thereinhighly stable long term properties of anticorrosiveness, decorationalappearance and low-electrical contact impedance comprising:

oxidizing said surface;

reacting the oxidized surface with an oil having an unsaturatedcomponent; and

removing any residue of said oil which has not been reactively absorbedinto said surface.

5. The process of claim 4 wherein the oxidizing step is accomplished byanodizing the surface.

6. A- process for forming conductive, anticorrosive and decorativeexterior surfaces in electrical equipment structures comprising:

preparing a structure having an exterior surface formed of a metal inthe class consisting of tin, lead, indium and alloys containing at leastone of the foregoing metals;

anodizing said exterior surface; and

reacting said anodized surface with a material having a constituent acidin the class consisting of: duodecanoic, octadecanoic, octadecadienoic,octadecatrienoic, eleostearic, licanic and docosoenic acids.

7. A process according to claim 6 wherein said step of anodizing ispermitted to proceed until said exterior surface acquires a black mattefinish of pleasing appearance and wherein said reacting step comprisesabsorbing said material into the anodized surface and removing anyexcess of said material; said reacting step yielding a surface compoundpossessing stable electrical properties of low-contact impedance in thefrequency range DC to 30 MHz. and uniform appearance throughout.

gggy UTE s'm'ms @FCE Patent No. 859 Dated February 29, 1972 Invenwfls)E. P. Damm, Jr. A. W. Grobin, Jr. E; H.- Herel,

D. A. Radovsky It is certified that: error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

[- Column 1, line 72, the word "duodecanoic" should be spelled-duodecenoic and the word "octadecanoic" should be spelledoctadecenoic-. Column 5, line 4, the word "require" should be -acquire.,Column 6, line 21, the word "duodecanoic" should be spelledduodecenoic-. Column 6, line 22, the word "octadecanoic" should bespelled -octadecenoic Signed and sealed this 2nd day of January 1973.

(SEAL) Attest:

EDWARD A'LFLETCHERJR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents @239 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIONPatent No. 3,645,859 Dated February 29', 1972 Inventofl s) E. P. DammJr. A. "W. Grobin Jr E. H. Herel D. A. Radovsky It is certified thaterror appears in the above-identified patent and that said LettersPatent-are hereby corrected as shown below:

Column 1, line 13, "PO970007 should be deleted. Column 2, line 48, afterthe word "compounds" insert -differing-. Column 3, line 68, after theword "control" insert --sample-.

Signed and sealed this 27th day of June 1972..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GO'I'TSCHALK Attesting Officer 7Commissioner of Patents 32 3 2 UNITED STATES PATENT swim vCERTIFICATE OFCORREC'EECN Patent No. 3,645,859 Dated February 29, 1972 Inventofls) E.P. Damm, Jr. A. W. Grobin, Jr. E.v H. Herel,

D. A. Radovsky It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

F Column 1, line 72, the word "duodecanoic" should be spelledduodecenoicand the word "octadecanoic" should be spelled octadecenoic-.Column 5, line 4, the word "require" should be acquire., Column 6, line21, the word "duodecanoic" should be spelled -duodecenoic. Column 6,line 22, the word "octadecanoic" should be spelled -octadecenoic- Signedand sealed this 2nd day of January'1973.

(SEAL) Attest: v

EDWARD I LFLETCHERJR. ROBERT GOTTS CHALK Attcsting Officer Commissionerof Patents

2. In electrical equipment an exterior panel and frame finish coatingcomprising a conductive compound formed by reaction of an anodized layerof a metal with an absorbed layer of a reactive oil wherein said metalis selected from the class consisting of tin, lead, indium and alloyscontaining at least one of these metals and wherein the said oil has anunsaturated constituent.
 3. Coating of claim 2 wherein said anodizedlayer is formed by anodic oxidization of a thin surface layer of saidmetal or metal alloy supported upon a substrate of another metal.
 4. Aprocess for treating surfaces composed of tin, lead, indium, or alloysformed from combinations thereof, in order to establish therein highlystable long term properties of anticorrosiveness, decorationalappearance and low-electrical contact impedance comprising: oxidizingsaid surface; reactiNg the oxidized surface with an oil having anunsaturated component; and removing any residue of said oil which hasnot been reactively absorbed into said surface.
 5. The process of claim4 wherein the oxidizing step is accomplished by anodizing the surface.6. A process for forming conductive, anticorrosive and decorativeexterior surfaces in electrical equipment structures comprising:preparing a structure having an exterior surface formed of a metal inthe class consisting of tin, lead, indium and alloys containing at leastone of the foregoing metals; anodizing said exterior surface; andreacting said anodized surface with a material having a constituent acidin the class consisting of: duodecanoic, octadecanoic, octadecadienoic,octadecatrienoic, eleostearic, licanic and docosoenic acids.
 7. Aprocess according to claim 6 wherein said step of anodizing is permittedto proceed until said exterior surface acquires a black matte finish ofpleasing appearance and wherein said reacting step comprises absorbingsaid material into the anodized surface and removing any excess of saidmaterial; said reacting step yielding a surface compound possessingstable electrical properties of low-contact impedance in the frequencyrange DC to 30 MHz. and uniform appearance throughout.